Bovine somatomedin (SM) from about 600 L of blood has been purified by means of acid/heat treatment, gel chromatography, and finally isoelectric focusing. Two activities were noted, one having a basic pI which was 350,000 times more pure than the laboratory reference material and another possessing a slightly acidic pI which was 150,000 times more pure than the reference material. Both components stimulate the in vitro uptake of 35S-Na2SO4 and 3H-thymidine by costal cartilage of hypophysectomized rats. In addition, a Cohn IV fraction has been obtained from the American Red Cross. This material has been purified about 1,000 times relative to the native Cohn IV material. The active principle is about 5- to 12,000 Daltons. BIBLIOGRAPHIC REFERENCE: Purification of Bovine Somatomedin, Liberti, J. P., Endocrine Society Meetings, Abs. 456, NY, NY, 1975.